This invention relates to a method of confirming, by simulation, whether or not a sequential operation control program for conducting sequential operations of equipment for a production line or the like operates as is intended to be designed, i.e., a method of composing a simulation program and a method of effecting simulation. More particularly, this invention relates to a simulation program composition method and a simulation method used in a case where the control program involves parallel operations.
A system of controlling a production line such as a motor vehicle assembly line is known which includes a sequential control unit incorporating a computer to effect sequential control of various equipment units provided for the production line with respect to operations which are to be successively effected by the equipment. To perform such sequential control, the computer incorporated in the sequential control unit is loaded with a sequential control program, and successively conducts steps of control of the operations of equipment units provided along the production line in accordance with the sequential control program.
For this kind of sequential control program, simulation for confirming whether or not the program operates in accordance with the program design is performed before the sequential control is actually conducted. To perform this simulation, in ordinary conventional systems, simulating input/output signals corresponding to the actual operations of the equipment units are applied from the outside.
Conventionally, to apply simulating input/output signals for the sequential control program from the outside, it is necessary to provide a multiplicity of switches or the like for producing simulating input/output signals, and the operator who operates the incorporated computer selects input/output signals which are to be applied and sets the order and timing of application of the selected input/output signals. This operation is troublesome. Also, since the switching elements or the like for producing the input/output signals are operated by a human operator, the kinds of phenomena which can be simulated are limited and it is difficult to examine the entire program.
Another problem with the conventional simulation method described below has been pointed out. Generally, in actual production lines, there is a unit block, namely a plurality of equipment units, which operates in parallel with other blocks. According to the conventional method, for simulation of a sequential control program for such unit blocks which operate in parallel with each other, the operation of the blocks are changed into the operations of serial blocks, and simulating operations are successively performed with respect to the equipment units. For example, where the operations of two blocks A and B are performed in parallel with each other, simulation of all the operation steps of the block A is first executed sequentially and simulation of all the operation steps of the block B is thereafter executed sequentially.
In the conventional simulation method, however, simulated operations are, of course, different from the actual operations since the actual parallel operations are simulated after being converted into serial operations. For this reason, it cannot be said that the conventional simulation method enables the program to be examined accurately. Moreover, it will take a long time to sequentially execute the simulation of parallel operations.